Prior portable vibrating concrete screeds of which I am aware have been of the type in which a plurality of longitudinally extending screed units are connectable end-to-end to form a screed of any of several possible lengths, depending on the lengths and number of screed units employed. Typically, a motor is mounted on one of the screed units to drive vibration-inducing shaft sections on the connected screed units. U.S. Pat. No. 4,030,873 (Morrison) defines an example of such a prior art screed.
It has also be known to mount a hand-powered winch on a fixed bracket at the end of the screed to advance the screed forwardly along the concrete area to be smoothed, the forward end of the winch line being fixed, as by stakes or the like, to the ground at some location ahead of the screed.
However, the portable, multi-unit, vibrating screeds of which I am aware have not been entirely satisfactory for a number of reasons. First, the bottom frame members of adjacent screed units have normally been connected together on the job site by through-bolting upstanding webs of the bottom rails of one screed unit to overlapping plates which are fixed to and extend longitudinally beyond the upstanding webs of the bottom rails of the adjacent screed unit. However, it is these bottom rails which engage and quickly become coated with concrete during screeding as do the bolts extending therethrough. Moreover, in order to maintain the portable screed units acceptably light in weight, the upstanding webs are necessarily relatively small and the through bolts are relatively small also, for example less than 154 inch diameter and typically 5/16 inch or 1/4 inch diameter. Accordingly, it becomes difficult and time consuming to release and reinstall these small bolts and their corresponding nuts, in view of the small size thereof, their correspondingly relatively fine threads, and their insertion through the concrete smoothing members.
Further, it is typical in the prior art to effect connection of adjacent screed units by moving one toward another longitudinally, in coaxial relation, until plates at the top and bottom frame rails and on the shaft section of one screed unit laterally overlap the ends of the top and bottom rails and shaft section on the adjacent screed unit. However, it is often difficult to achieve the desired alignment of two bottom rails, one or two top rails and a shaft section of one screed unit with the corresponding parts of the adjacent screed unit while longitudinally pulling into position one of the relatively long and bulky screed units. Moreover, it is also difficult and time consuming to align bolt holes in the various members simultaneously to allow through-bolting.
In addition, depending on conditions, a pair of screed units may tend to either sag or buckle upwardly at their connected ends and it is difficult to overcome this tendency and maintain precise coaxial alignment of adjacent screed sections with a simple through-bolting of overlapped frame rails or, as in aforementioned U.S. Pat. No. 4,030,873, with a simple pressure clamp arrangement for joining the top frame rails.
In addition, means for adjusting the vibration amplitude on prior art screeds of which I am aware have not been satisfactory and it is typical, as in the aforementioned patent, to not provide for any such adjustment, despite the fact that the ability to adjust vibration amplitude is desirable to adapt the screed to varying conditions of weather, concrete thickness and stiffness, and the like.
Further, on prior art screeds of which I am aware, the motor has normally been mounted on the endmost screed unit, which also typically has nonremovably fixed thereon the winch mount. Accordingly, the motor cannot be located, should such be desired, in the middle of the assembled screed. Furthermore, the winch mount cannot be relocated along the length of its particular screed unit nor can it be mounted on other screed units comprising the completed screed.
The objects and purposes of this invention include provision of a lightweight, portable, knock-down, multiunit screen which can be assembled on a job site and adapted to the conditions at hand, and which, subsequently to completion of the screeding operation, can be disassembled for shipping to another job site, all with minimized input of time and labor, so as to minimize time and labor costs for the screeding job as a whole, particularly when screeding relatively small concrete areas wherein actual screeding time is relatively short.
A further object of this invention is to provide a screed as aforesaid in which the screed units are connected by quick change connectors not requiring tools, which are relatively unaffected by engagement with concrete, and which are positively adjustable to control upward or downward bowing of the screed at the interconnection of screed units. A further object is to provide an apparatus as aforesaid in which screed units are joinable by transversely dropping the end of one upon the adjacent end of another, wherein, without more, the adjacent screed units are fixed with respect to each other in a horizontal plane, both longitudinally and transversely of the screed.
A further object of the invention is to provide a screed as aforesaid in which the screed unit supporting the motor can be located at any desired location in the multi-unit screed, and in which a winch support may be located at any of several permitted locations on a given screed unit or on any desired one of several screed units.
Further objects and purposes of this invention will be apparent to persons familiar with apparatus of this general type upon reading the following description and inspecting the accompanying drawings.
The objects and purposes of the invention are met by providing a knock-down vibrating screed comprising elongate screed units attachable at and in a longitudinally extending row to provide a screed of desired length. Ones of the screed units each comprise an elongate frame unit movable transversely over the concrete and vibration means for vibrating the corresponding frame unit for smoothing the concrete over which the frame unit moves. The adjacent ends of the screed units positively block strictly coaxial longitudinal movement of adjacent screed units into attached relation with each other. The adjacent ends of the screed units block strictly coaxial longitudinal movement of attached screed units out of attached relation with each other. Further, the adjacent ends of adjacent screed units are attachable by longitudinal overlapping, followed by movement one toward the other in one direction transverse to the length of the screed into an attached position of longitudinal coaxial alignment in which the longitudinally overlapped ends positively block further movement in the one transverse direction.